Blade-bracing and method of locating the same



C. E. SEARCH.

BLADE BHACING AND memoo or LOCATING THE SAME.

APPLICATION FILED 18.16.1918.

Patented July 15, 1919.

THE COLUMBIA PLANOORAPH cm. WASHINGTON, n. c.

UNITED STATES PATENT OFFICE.

CHARLES EDWIN SEARCH, OF MILWAUKEE, WISCONSIN, ASSIGNOR TO ALLIS- CHALMERS MANUFACTURING COMPANY, OF MILWAUKEE, WISCONSIN, A

CORPORATION OF DELAWARE.

Specification of Letters Patent.

Patented July 15, 1919.

Application filed February 16, 1918. Serial No. 217,985.

To all whom it may concern:

Be it known that I, CHARLES EDWIN SEARCH, a citizen of the United States of America, residing at Milwaukee, in the county of Milwaukee and State of Wisconsin, have invented a certain new and useful Improvement in Blade-Bracings and Methods of Locating the Same, of which the following is a specification.

This invention relates to improvements in the construction of steam turbines and particularly to improved means for bracing relatively long and thin steam turbine blades, and to a method of determining the most eflicient location of such means.

An object of the invention is to provide eificient means for bracing turbine blades. Another object is to provide a simple method of'determining the most eflicient location of the blade bracing means.

It has heretofore been customary to stiffen or brace relatively long turbine blades in order to prevent fracture thereof due to vi bration, by connecting the successive blades at points intermediate their ends by means of a strip or ribbon of metal which was secured to the blades either by distorting the bracing strip or by fusion of metal. It has been common practice to arbitrarily osition the bracing strips of the prior art, t e usual location of the strips being' midway between the ends of the projecting portions of the blades. While these bracin strips of the prior art strengthened the ilading, it has beenlfound that by positioning the bracing strip at definite points along the lengths of the blades, a structure of maximum rigidity and strength results. The most efiicient location of the bracing strip may be definitely ascertained by making break-down vibration tests of similar segments of blades, each having the bracing strip located at a different distance from the blade roots. As an example embodying theresults of such test, it has been found that for blades of approximately 7%" len th the most efficient location of the strip is etween onefourth and one third of the blade length, from their rests A clear conception of an embodiment of the invention may be had by referring to the drawing accompanying and forming a part of this specification in which like reference characters designate the same or similar parts in the various views.

Figure l is a transverse section through a rotor blade segment, the section being taken along the line 1-1 of Fig. 2 looking in the direction of the arrows.

Fig. 2 is a side elevation of a rotor blade segment showing a segment of a bracing strip properly located.

Fig. 3 is a transverse vertical section through, the shroud, bracing strip, and foundation ring segments, the section being taken between two successive blades.

Fig. 4 is a curve adapted for use in deter mining the most eflicient exact location of the bracing strip.

The rotor turbine blading of which a segment only is disclosed in the drawing, comprises a foundation ring segment 4:, a shroud ring segment 5, a bracing ring segment and a plurality of radial blades 2 interconnecting the ring segments. The blades 2 are rigidly secured at their roots to the foundation ring segment 4 in any suitable manner, the blade roots in the present case being secured b fusion of metal by casting the metal of t e ring segment 4 directly around the blade roots. To the outer opposite ends of the blades 2 is rigidly secured the shroud ring segment 5 in any suitable manner, as by fusion of metal by brazing. The brazing ring segment 3 is rigidly secured to the thicker inlet edges of the blades by first notching these edges and inserting the ring segment within the notches, and then brazing or otherwise securing the ring segment 3 to; the blades at their notched portions. The entire blading segment istherefore constructed as an integral, rigid, element which may be secured to the turbine rotor in any suitable manner as by calking, bolting or otherwise securing the same.

In determining the most efiicient dint of location of the shroud ring, it is esirable l the brncin to construrt a number of sample blade segments which are of like construction throughout except for the location of the bracing ring segment 3. This bracing ring segment 3 is located at different distances from the blade roots in the Various sample segments. The segments are then subjected to like break-down tests by vibrating the segments in a direction a pmxirnatelf pondienlar to the blades, that is, across t eir thickness. As the blades 2 are set at an angle to the shroud and foundation rings 5, 4, this vibration will also e in a IIGEtlOH Hi an angle to the plane of these rings. The Vibration of the sample segments is continued until the blades 2 break, it being found that the blades generally break at or near the root ends thereof By comparing the number of vibrations or the length 0 time necessar to fracture the blades of the various samp es, approximately the most eflioient point of location of the bracing strip is ascertained.

In order to ascertain exactly the most ellioient point of location of the bracing strip other samples having the bi'aCing strip incaied in the vicinity of the loetio-h of the strip producing the best results under the preliminary test, may be subsequently tested and the one selected showin the best results. The same result may also 9 a/r riied at by lotting a curve such at shown in Fig. 4, having the tinie of vibration to breawdown as one coordinate and having location of strip alon the bl'atle'length in inches as be other or rdinate. This turn: will rapidly reach a maximum pflitlto f time value and as rapidly rorede therefrom. The point in question is therefore sharply defined.

It has been found by actual ex erimeht that locating the strip at this ines eilloient point of location of the bracing strip 6 prolongtofreatly the life (if the binding. As heret ore stated, it has also beenfotnd that the most elficieni. location of the bracing strip is slightly more than Ode-Muith the length of the blades from the fbundation ring for a given length of blades; In all bases it has been fountlthat memostemtieht location of this bracing strip 8 is use than one hali the length of the blades from: the

. sha es of blades, tile piesent inventitn is up foundation rin' While the exact rotation may differ slig ay for diiferent types and 6 position of the bracing ship. it sheila-bewilderment that it is hot rle sired have limited to unmet deans (if donstruction' herein assented for various modifications viii occur to a persmrskflled iieebie in all cases w properly ioeate t most efficient in the tlrti n is claimed and desired to secure by ten; Potent-i y 1; In cambinmmi, a piuraiity of Blades rigidly secured at corresponding ends to a foundation element, and bracing means cooperating with said blades intennediate their ends. said bracing means constituting the sole interntediam support and being benearer the fixed blade ends than the Opposite ends of said blades.

2. In combination, a plurality of blades rigidly seoured at corresponding ends to a toiind'ation element, and Vii/oi means cooperating with said bla intermediate their ends, said braoing means constituting the sole intern'iediate support and being less than one-third the length of the blades from t eir fixed ends.

Ill emnblnation a plurality of blades rigidly secured at corresponding ends to a foundation element, and bracing means eoopemitin with said Blades intermediate their 61159 said bracing rlleahs consbitlltihg the sole intermediate support and being between ones-third and one- ,ourth of the length of the blades from tlieii flied ends.

4. In mmbiI atiUn, a plurality of blades rigidly sebilred at corresponding ends to a foundation element, and bracing mean eooperating with said blades intermediate their ends, said bracing means constituting the sole intermediate support and beinglj'etween one-third and GHQ-fifth of the length (if the blades froth their fixed ends.

5. In combination, a plurality of times rigidly set-arm at correeponfiin ends to a foundation element, and lemon means atoperating with said blades intermediate their aids, said bracing means eons'tltfiting the sole intermediate sip 61% and being between one-half and one-Etch of the length of the blades fi'bln their fixedends.

6. In combination, a pluralit of blades rig-idl soe'ured at their rims, and bracin means cooperating with Said blades intermediate their ends, aid bracing means constituting the sole intei-hfe late support aha being approximately one oilrth the length of the blades from their mob ends,

7. Iii co-ni'biha-tibil, a lurality of blades 1*" idly SCllI'H as each other attheifoposi it ends, and brsleihg means rigidly seeuiag to said bladesfihteflhediate their ends at biaolflg means constituting the 861( lfltfi-fmeditate hpiaoit and being 8P roximately one-fauna t 6 length of the lanes has; their correspo-fifiing nds.

8. In combination, a plurality of rigidly settled at corresponding e s, an 1 and '9; means smi ed to th nlet gee oi said lades intjt rihedlm their ride, Sal braelh means". i h aearerfliej Xedblaje ehds'tl ian a at ite'en ls e and ti,"

. a In eofn inatbn, aipmalt of t s iigldlyfsechfed at d bf'rfififnding ends to a out than element an main eans seclliec the lnlet'd is of sai' lit r mama their 'fitis; and bite ans ing less than one-third the length of the constituting the sole intermediate support blades from their fixed ends. for said blades and being nearer said foun- 10. In combination, a plurality of radial dation segment than the opposite ends of 10 blades rigidly secured at corresponding said blades. 5 ends to a segmental foundation element, and In testimony whereof, the signature of the bracing means coiiperating with said blades inventor is affixed. intermediate their ends, said bracing means 0. EDWIN SEARCH.

copies of this patent may he obtained for five cents each, by addressing the "Gommissioner of Patents. Waahlngton, D. 0." 

